Computed transaxial tomography techniques have recently been disclosed and developed. In particular there has recently been disclosed and claimed apparatus for producing circularly scanned charged-particles which, when striking a target, produce a rotating x-ray beam suitable for use in computed transaxial tomography. Such devices can operate using any one of a variety of beam scanning apparatus which are well known in connection with cathode-ray oscilloscopes, radar, etc. However, a major use of circularly scanned beams is for the production of fast x-ray scans, as in the case of taking x-ray "pictures" of moving objects, such as a human heart. Such fast x-ray scans require a rapidly scanned charged-particle beam, and if such a beam is to produce x-rays of adequate intensity, high beam currents must be employed. Because of space charge effects and other phenomena, the need for high beam currents automatically requires that the beam have a relatively large cross-section at the place where it is deflected. The beam must then be focused so as to converge strongly at the target in at least one dimension, so as to provide high resolution. The deflection and focusing of such high-current, large-cross-section beams requires a radically different approach from those taught by the prior art.